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Book _T-S^Bl5. 



FURTHER NOTES ON THE NATURAL HISTORY AND 
ARTIFICIAL PROPAGATION OF THE DIAMOND-BACK 
TERRAPIN :::::::::::: By R. L. Barney 

From BULLETIN OF THE BUREAU OF FISHERIES, Volume XXXVIII, 1921-22 
Document No. 917 : ; ; ; ; ; ; ; Issued April 24, 1922 




PKICE, S CENTS 
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FURTHER NOTES ON THE NATURAL HISTORY AND 
ARTIFICIAL PROPAGATION OF THE DIAMOND-BACK 
TERRAPIN :::::::::::: By R. L. Barney 

From BULLETIN OF THE BUREAU OF FISHERIES, Volume XXXVIII, 1921-22 
Document No. gif : : : : : : : : : : : : : Issued April 24, 1^22 




PRICE, 5 CENTS 
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LIBRARY OF CONQKISS 
sEceiveo 

JUN3 1922 

DOCUMENTS DIVISION 



FURTHER NOTES ON THE NATURAL HISTORY AND ARTIFICIAL 
PROPAGATION OF THE DIAMOND-BACK TERRAPIN. 

By R. L. BARNEY, 
' Director, U. S. Biological Station, Fairport, Iowa. 

CONTENTS. 

Page. 

Introduction gi 

Brood stocks of the experimental farm 92 

Original Carolina brood stock 93 

Second Carolina brood stock , 54 

Texas brood stock 95 

Ratio of sexes and fertility' 96 

Growth 98 

Attainment of salable size 100 

Culling 100 

Winter feeding loi 

Space requirement 102 

1909 brood 103 

1910 brood 104 

191 1 brood 105 

1912 brood 106 

1913 brood 107 

1914 brood 108 

Mortality ^ 108 

Summary no 

INTRODUCTION. 

There appears to have been sufficient progress made in the experimental work on 
the artificial propagation of the diamond-back terrapin, Alalaclemmys centrata, at the 
United States Fisheries Biological Station, Beaufort, N. C, since 1915 to warrant the 
drawing up of a report covering such information on this subject as has been collected 
to date and has remained unpublished. In Economic Circular No. 5, revised, of the U. S. 
Bureau of Fisheries,' the results of observations up to and including 19 15 are cited with 
methods outlined for construction of pens, selection of brood stock, care of eggs, young, 
and adults, and some notes on the growth of the terrapins. Much information has been 
collected since that time by continuing observations on many of the same terrapins 
considered in the 19 17 report and also through further studies with dififerent purposes 
begun in more recent years. 

' Hay, W. P.: Artificial Propaeation of the Diamoad-Back Terrapin. Economic Circular No. 5. revised. U. S. Bureau of 
Fisheries, Washington, 191;. 

91 



92 



BULLETIN OF THE BUREAU OF FISHERIES. 



The terrapin propagation study has been directed since its beginning by several 
investigators. Originally Dr. R. E. Coker gave his attention to its possibilities and 
prepared a report of his results for the North Carolina Geological and Economic Survey.^ 
At the same time Prof. W. P. Hay began similar investigations in Chesapeake Bay. 
In 1909 these were transferred to Beaufort, where Dr. Hay took charge of the experi- 
mental work and continued giving it his du-ection from 1909 to 19 15. During this 
time H. D. Aller planned and carried out the feeding of yearling terrapins during the 
winter in a warmed nursery house. Lewis Radcliffe relieved Mr. Aller in 19 12 and was 
later followed by S. F. Hildebrand. Some of the material herewith discussed is from 
experiments begun by the two last-named investigators, but left unfinished because of 
their removals from Beaufort. The present paper is based on the unorganized notes of 
each of the above-mentioned investigators and also on the systematic observations 
carried on under their supervision by Charles Hatsel, the terrapin culturist stationed at 
Beaufort, N. C, since the experimental work was begun. The large share of credit for 
the continuity and the accuracy of the observations of the entire experimental terrapin 
propagation project is due Mr. Hatsel for his exceptionally careful, energetic, and 
faithful work. The writer has had the direction of the experiments since the fall of 
1919. B. J. Anson has assisted in organizing and tabulating the data discussed in 
this paper and J. B. Southall has prepared the graphs. 

BROOD STOCKS OF THE EXPERIMENTAL FARM. 

The terrapins of the original brood stock, which are either the parents or grand- 
parents of all the Carolina terrapins that are held in captivity and imder observation 
at the Beaufort station, were purchased in two lots, the so-called "original lot of North 
Carolina breeders " and the " second lot of North Carolina breeders." To these was added 
later, but kept separate, a number of adult Texas terrapins as brood stock. The pro- 
duction in eggs and young throughout the years of captivity of these terrapins is herewith 
tabulated (Table i) and shown in graphic form (fig. 76). 

Table i. — Records op Breeding Stocks of Terrapins in Captivity at Beaufort, N. C. 



Stock and year. 



Original stock: 

1909 

1910 

1911 

1912 

1913 

1914 

191S 

1916 

I9I7 

1918 

1919 



Males. 



Females. 



Eggs. 



Young. 



Number. 



j88+ 

598+ 

638 

732 

736 

923 
921 

722 

*757 
*834 



Y^r Number. 



(?) 
6.S + 

"3-9+ 

16.0 

17.0 

18.8 

23. 6 

23. 6 

18.5 
' 19. 4 
'21.3 



288 
598 
538 
610 
594 
836 
8>3 
639 
"675 

'' 7.';7 



Rate per 
female. 



" Five males taken from this lot for experimental purposes in 1911 were returned to it in 1919. 
* Estimated. 



(?) 
6. s 
13.9 
12. s 
14 I 
15- 2 
21.4 
20. 8 
:6.3 
'' 17-3 
*■ 19.4 



Per cent 

eggs 
hatched. 



(?) 
(?) 
(?) 

78. 

88. 

8a. 

90. 

88. 

83. 

"90. 



'Coker, R. E.: The Cultivation of the Diamond- Back Terrapin. 
Raleigh, 1906. 



Bulletin No. 14, the North Carolina Geological Survey. 



THE DIAMOND-BACK TERRAPIN. 93 

Table i. — Records ok Breeding Stocks of Terrapin in Captivity at Beaufort. N. C. — Con. 



Stock and year. 



Males. 



Second stock 

1911 

1912 

1913 

1914 

191S 

19x6 

1917 

1918 

1919 

1920 

Texas stock: 

1912 

1913 

1914 

191S 

1916 

1917 

1918 

1919 

1930 



45 
4S 
45 
45 
45 
29 
29 
28 
27 
kjo 

d j2 
d29 
d 29 
d 29 
d 12 



Fenaales. 



Eggs. 



Number. 



649 
673 

745 
958 
871 
"973 
''731 
" 773 
1. 172 

127 
292 
412 
399 
421 
497 

270 
138 



Rate per 
female. 



90 

9-4 

10.4 

>3-4 

13-6 

«l5-4 

« II. 5 

" "5.4 

•■13.1 

3-7 
8.5 
12. I 
11. 7 
J6. 8 
19.8 

C) 

24. 5 
'12-5 



Young. 



Number. 



583 

606 

724 

876 

783 

80s 

"670 

1 702 

1. 133 

lOI 

281 
376 
366 
383 
439 

2-17 
131 



Rate per 
female. 



8.3 
8.6 

10. 2 
12-5 

12. 2 
12-7 

o 10. 6 
« 14. o 
* 12. 7 

2.6 
8.2 

11. o 
10. 7 
15-3 
17- 5 

(0 

22. 4 
f 12. I 



Per cent 

eggs 
hatched. 



89.8 

90.0 

97-1 

91,3 

89.8 

l>82. 7 

l> 93. o 

l>90.8 

96.6 

79- S 
96. 2 
91- 2 
91- 7 
90.9 
88.3 

91.4 
97.0 



1 Estimated. 

b The 1920 record represents the combined production of the original and the second brood stocks. The penning together 
of individuals of both stocks made it impossible to ascertain the production of either stock. 

<^ Decrease in production probably due to destruction of epgs by rats. 

•^ This record for males includes five Carolina original stock males used in hybridization studies. 

' Records for production not obtamed on account of storm which destroyed egg beds and washed many small and adult 
terrapins from their inclosures. 

ORIGINAL CAROLINA BROOD STOCK. 

Considering the original or first lot of breeders it will be noted that highest egg 
production occurred in 19 15 and that since then the egg rate per female, with exactly 
the same number of females laying, has diminished by from three to five eggs. The 
percentage hatched has varied but slightly. This, however, would be reasonably 
expected with the same number of males on hand and the number of eggs to be fertilized 
somewhat less. In view of the fact that egg production has fallen off since the 1916 
production and remained under that high mark now for four years through 1920, it 
seems probable that the period of maximum egg production in this brood has passed. 
However, the slight increase during 19 18 and 19 19 perhaps means that the brood 
may still reach greater egg production than its maximum egg record of 19 15. Still 
beneath the maximum mark, it may also indicate that certain females are about to 
reach maximum production while others have passed this point. The heavy falling off 
in recorded egg production in 1920 (see figures for 1920 under second stock in Table i) 
was due to the depredations of rats which dug up many nests and destroyed hundreds 
of eggs before control methods were effective. The 1920 figures, therefore, do not 
represent the possible egg production and hatch, for the record of eggs laid would 
doubtless have been verj'^ much higher had it not been for the destruction caused by 
the rats. 

The average size of the females of this lot in 1911 was 154 mm.' Considering what 
is known of the history of some of the individuals of this lot since 1902, their size then 
and their growth suice, it appears probable that at the time of their measurement in 
191 1 they averaged close to 20 years of age. The estimated age of these terrapins is 



' Approximated from measurements recorded in inches. 



94 BULLETIN OF THE BUREAU OF FISHERIES. 

arrived at from a knowledge of their size at the time of their purchase and of the num- 
ber of years during which they have been captive in the experimental pens. They were 
all adults at the time of their purchase, and the approximation of their age must be 
quite accurate. From the knowledge that it takes at least much longer than nine 
years for hibernating terrapins to reach an average length of 142 mm. (see Table 3) 
and that after the length 142 mm. is reached the average annual growth increment is 
not more than 1.5 mm., it appears reasonable that the age of the terrapins of this brood 
was at least 18 years in 191 1 (the year of measurement). 

Years. 

To reach average length of 142 mm g 

To grow from 142 to 154 iiira. (the 1911 average length) 9 

From 191 1 to 192 1 10 

Total average age in 192 1 28 



24 
20 
16 
12 
8 
4 




































/ 


/ 


\ 




/ 


\ 












^ 


^ 










\. 








r 


^^^ 






^v 




\ 


\ 




v\. 




/ 






/. 










^y 






f 


/ 




/ 


/ 
















/ 

























1909 1910 1911 1912 1913 J914 1915 1916 1917 1918 1919 1920 

Fig. 76.— Egg production per female in original and second Carolina and Texas brood stocks. .Original Carolina brood 

stock; , second Carolina brood stock; , Texas brood stock; * combinetj egg production per female of 

original and second Carolina brood stocks. Marked decrease in egg production probably due to destruction of eggs by rats. 

Inasmuch as maximum recorded egg production for this lot occurred in 191 5, we 
may presume, then, that maximum egg production occurs about the twenty-fifth year 
of a terrapin's life. The actual maximum production of young, however, would, of 
course, depend on the presence of sufficient males among the breeding stock. 

SECOND CAROLINA BROOD STOCK. 

The second lot of North Carolina breeders, with average measurement of •141 mm.* 
ill 191 1 and probable average age of 9 years, has shown, with tfie exception of the years 
1918 and 1920, a general increase in egg production since the begiiming of its laying. 
The 19 1 8 record showed a dropping off in egg production of 2.1 eggs per female. The 
reason for this decrease is problematical, but the exceptionally severe winter of 1917-18 
and the following late spring, with its resulting longer hibernation period and its retard- 

' Approximated from measurements recorded in inches. 



THE DIAMOND-BACK TERRAPIN. 95 

ing influence on normal spring feeding and growth in the terrapins, may possibly be 
the causes of the decreased productiveness, though a similar dOTrease is not found in 
the egg production of the original brood stock. The 1920 decrease shown in Table i 
is due in part to the destructiveness of the rats above referred to and probably also 
to a very late spring, the first eggs being laid on May 17, a rather late date. Many 
of the brood terrapins, however, did not lay their first eggs of the season until the mid- 
dle of June, more than a month after the usual first egg-laying date. In 191 7 certain 
of the females of the second lot of breeders were set aside for experimental purposes, 
and this had a tendency toward diminishing the actual number of young produced, 
while the experiments yielded information which is of value from other aspects and 
will be discussed later. Because of this experimental work the figures for "young" 
in the table are estimates and are included only tentatively in the 1918 and 1919 records. 
The mixing of part of the first lot with the entire second lot of breeders in 1918 and 19 19 
made it necessary also to estimate the number of eggs laid by both these lots, and these 
records have been so noted. 

The estimation was possible in view of the fact that a considerable proportion of 
the original brood stock was not mixed with the second brood stock. The method 
followed to obtain the estimated records was this. One lot of the original brood stock 
(lot A) was held in a separate pen during the year, and from the egg and young produc- 
tion of this lot was computed an average egg and young production for the entire original 
brood stock. From this computation it was possible, then, to figure the production 
of those terrapins (lot B) of the original brood stock which had been penned with the 
second brood stock. The egg and young production of the entire second brood stock 
(lot C) was ascertained by subtracting the egg and young production of lot B from the 
total egg and young production of lots B and C combined, lot B plus lot C representing 
the mixed lots of brood stock. 

In 1920 the terrapins of the first and second lots of breeders were so mixed that it 

was impossible to estimate at all accurately the egg production of either lot, and for 

this reason the egg production and hatch of these broods for 1920 are combined. The 

combined egg and young production record, though lower than that of either lot in 

the preceding year, is not significant, however, because of the heavy egg destruction 

caused by rats. 

TEXAS BROOD STOCK. 

The Texas brood stock, with average lengtli in the spring of 1920 of 177 mm.^ and 
probable age of 30 j'ears, has shown an increasing productiveness annually since its first 
laying in confinement until 1920, when doubtless, as abo\-e, the decrease in the egg and 
young production record was due to destruction of eggs by rats. In 1919 from 1 1 adult 
females of this stock which had been used in hybrid studies with Carohna males there 
were obtained 270 eggs, or 24.5 eggs per female. In 1916 all but 12 of the Texas terra- 
pins were returned to Texas. The 1 2 that remained were the finest and largest females 
of the original Texas lot, and the exceptional egg production of the 1 1 mentioned above 
may be due to this fact. It is understood that when the entire Texas brood stock was 
at Beaufort the average number of eggs produced per female was lower than for either 
of the Carolina lots. 

* Approximated (rom measurements recorded in inches. 



96 



BULLETIN OF THE BUREAU OF FISHERIES. 



It is noteworthy in this connection that this maximum production for the Texas 
stock is greater than that of the Carolina breeders. The maximum records of the two 
stocks are as follows: Carolina, egg rate, 23.6; young rate, 21.4. Texas, egg rate, 24.5; 
young rate, 22.4. 

The excessively cold winter of 1917-18, which apparently slowed down output 
among the second brood stock of Carolina terrapins, did not effect any retardation in 
the productiveness of the Texas stock. The heavy decrease in recorded productiveness 
of this brood stock in 1920 is due to destruction of eggs by rats, as in the case of tlie first 
and second lots of Carolina breeders. 

RATIO OF SEXES AND FERTILITY. 

The number of males in a given stock of brood terrapins in each of these experimental 
lots has been about one-third to one-half the number of females present. There appears 
to be a negligible difference in the rate of young hatched per female in the different 
broods with differing percentages of males present. A normal hatch appears to be about 
90 per cent of the eggs laid, no matter how great a number of males may have been pres- 
ent. It is needless to say that scarcity of males would, of course, increase the number 
of infertile eggs laid. This percentage of infertile eggs is much larger at the beginning 
of the laying period (fig. 79) of the terrapins and at the beginning of captivity (Table i). 

The cause of the high infertile egg rate among terrapins which have laid for the first 
time under our observation and have been penned with male terrapins of exactly their 
age throughout their lives may be found in the fact that possibly the males do not reach 
sexual maturity as early as the females. This is indicated in a study of certain lots of 
terrapins experimented with during 1919. Seventy-eight female terrapins of the 1914 
brood which had never laid fertile eggs, due to the fact that males had never been penned 
with them, were separated into two equal lots which were kept in separate pens. With 
one lot of 39 females were placed 3 males of the original brood stock at least 25 years 
old; with the other lot were placed three 5-year-old males of the 1914 brood. This 
division of the lot and introduction of males occurred on the same day in early spring, so 
that there might be plenty of opportunity for fertilization to occur before the egg-laying 
period arrived. The production was as follows : 





Females. 


JIalcs. 


Age of 
of males 
(years). 


Eggs 
laid. 


Eggs 
hatched. 


Per cent 
fertile 
eggs. 


Percent 

infertile 

eggs. 




39 
39 


3 
3 


5 

2S 


'45 
187 


54 
152 


22. 
Si. 2 


;.1.o 




18. S 







It is suggested from these data that males of 5 years are less potent than much 
older ones and that maximum fertility may not be expected where >oung males, just 
reaching sexual maturity, are used. 

In reviewing the entire matter of the most desirable numerical relation of males to 
females in this species, it should be pointed out that mating among terrapins is pro- 
miscuous. Copulation in one year may mean the production of fertile eggs for more 
than that year alone. To cite a case under our observation, in 1914, 10 females of the 
second lot of Carolina breeders which had been producing young were set aside in a 
separate pen without males- With no furtlier association with males, these terrapins 



THE DIAMOND-BACK TERRAPIN. 



97 



laid fertile eggs each subsequent year until and including 191 8. The record of egg 
production and hatch of these 10 terrapins through 191 8 is as follows: 





Eggs. 


Young. 


Percent 

infertile 

eggs. 




Eggs. 


Young. 


Per cent 

infertile 

eggs. 




129 
116 


12S 
102 


c. 7 
12.0 




130 
108 


39 
4 






f 1918 


96. 2 









In the spring of 1919, 5 males were introduced into this lot, and the fall produc- 
tion was 137 young from 146 eggs. From this experiment it appears that female ter- 
rapins may retain live spermatozoa in a healthy condition after a single copulation as 
long as four ) ears, and under such conditions some eggs laid even in the fourth year may 
be fertile. It is apparent also that fertilization may occur immediately after copulation. 

In further consideration of the proper ratio of sexes for maximum fertility we have 
the records of several domestic broods (Table 2) which, it happens, have contained 
fixed ratios of males per 100 females throughout their existence. This set of observa- 
tions includes lots in which the males number 5, 9, 12, 24, 32, and 50 per 100 females, 
and the records give some suggestion of what may possibly be the most desirable ratio 
of males to females to produce maximum fertility. 

Table 2. — Sex Ratio and Fertility of the Diamond-Back Terrapin in Captivity. 



Egg-laying year. 


Males. 


Fe- 
males. 


Males 
per 100 

fe- 
males. 


Eggs 

laid. 


Per 

cent 
fertil- 
ity. 


Egg-laying year. 


Males. 


Fe- 
males. 


Males 

per 100 

fe- 
males. 


Eggs 
laid. 

13 
348 
572 
606 

952 
398 

8 
7 
470 
6S3 
983 
621 

127 
188 


Per 
cent 
fertil- 
ity. 


1909 hibernated brood; 
First 


8 
8 

3 

3 

2 
2 

,■; 
5 
.I 
S 
5 

8 
8 
8 
8 
8 
8 


89 
89 
89 
S, 
89 

=5 

-S 

2.> 

=5 
as 


300 

30O 
50 
.SO 
.iO 
50 

,■; 
5 
s 
s 
,<; 

.1- 
3' 
32 
32 
33 
32 


06 
118 

98 
119 

I.!8 

140 

38 

260 

452 
640 
421 

27 
418 
529 

S26 

67S 
467 


77-8 
63. S 
73.4 

95- 7 
94-7 
89.2 

97-4 
82.4 
93- 2 
75- 
61.2 

9I- 2 

95- 5 
91. 5 
95- 7 


1910 wnter-fed brood: 
First 


10 
10 
to 
10 
9 
9 

10 
10 
10 

10 
10 
10 

18 
.8 


140 
107 
107 
J04 
103 
103 

82 
82 
83 
82 
82 
82 

43 
43 


8 
9 
9 
9 
8 
8 

12 
12 
12 
12 

13 

12 

24 
24 


100. 






83.3 


Third 


Third 


78.6 








Fifth 


Fifth 


75. 4 


Swth . 


Sixth 




1910 hibernated brood: 
First 


J9H winter-fed brood: 
First . . 










Third 


Third 




Fourth 


Fourth 




Fifth 


t'lth . . 


84.6 






88.8 




1912 ^vinter-fed brood: 
First 






91. 4 


Third 


Second 


85. 1 


Fourth 

Fifth 






Sixth 









In viewing the records of these broods it is necessary to bear in mind that maximum 
fertility does not occur in the first year of laying in any brood unless there happens to 
be laid only a very few eggs which may have, by chance, become fertilized. Accepting 
90 per cent as normal fertility, it will be noticed that this per cent of fertility was reached 
in the 19 10 hibernating brood in the third year of laying, and that this brood contained 
only 5 males per 100 females. However, in the following year, when there were about 
200 more eggs laid, the per cent of fertility dropped to 75. The fifth year, though 
showing a decrease in fecundity in the terrapins, shows another considerable lowering 
of percentage fertility. A similar drop in the per cent of fertility is also found in the 
fifth and sixth years of laying of the 19 10 winter-fed brood after it had reached at least 
90 per cent fertility in previous years. It was accompanied in the fifth year by an 
7(5374°— 22 2 



9^ BULLETIN OF THE BUREAU OF FISHERIES. 

increase of 346 eggs to be fertilized. The 1911 winter-fed brood in its fifth year of 
laying also showed a decreased fertility of approximately 9 per cent, with an increase 
of 301 in number of eggs to be fertilized. Even with a smaller number of eggs by 362 
to fertiUze in its sixth laying year there was only a 4.2 per cent increased fertiHty, 12 
males being present throughout the observations. 

To be compared with these records there are the 19 10 selected brood and the 19 12 
winter-fed brood. These contained, respectively, 32 and 24 males per 100 females. 
The lot with 32 males per 100 females has yielded better than 90 per cent fertility now 
for the past four years, even though the egg production with the exception of the last 
year has increased yearly during this period. This is an especially good record in view 
of the fact that the egg rate in this lot in 1919 averaged 27.1 per female. The 
1912 winter-fed brood, with 24 males per 100 females, has laid but twice, and it is 
needless to say the record of these first two years may not be indicative of the future 
record of this group. However, the egg production was very large for the first laying 
year, and the percentage of fertility of the eggs in this case may be of considerable 
comparative value. This record is the highest of our observations for percentage of 
fertility in the first year where there has been substantial egg production. It will be 
noted, however, that with an increase of egg production in the second year the per- 
centage of fertility declined to 85.1 per cent. 

The 1909 brood, in which there are half as many males as females, has given during 
the past three years a high record. There is no doubt that there are more than enough 
males in this lot, since tlie 19 10 select brood has a record equally as good in percentage 
of fertility and contains only 32 males per 100 females. 

From our table and this discussion it seems warranted to conclude that after the 
brood has established a substantial egg-laying record a 90 per cent fertility mav be 
obtained with from 24 to 32 males per 100 females. The record of the 191 1 hibernated 
brood is good with only 12 males per 100 females. This record may be influenced, 
however, by the fact that appreciable egg laying in this brood was relatively late, 
coming in the ninth year, and thus much more time for copulation was available with 
but very slight utilization of the spermatozoa. 

GROWTH. 

Many data at hand concerning feeding and growth and their bearing on the develop- 
ment and functioning of the sexual organs of the terrapin are of value to the commercial 
terrapin culturist. The several annual broods, the offspring of the original and second 
lots of breeders, have had chosen from them certain numbers of individuals which have 
received varying treatments, the results of which can be compared to advantage. 

The effect of hibernation on the growth of the small, newly hatched terrapin is con- 
siderably different from that of winter feeding in a warmed nursery house. Whereas 
the hibernated terrapin grows none during the winter, the fed terrapins may make 
considerable growth. The food used and the temperature at which the terrapins are 
kept appear to be the factors most influencing growth in the nursery house. The heat- 
ing plant employed at Beaufort is merely a large coal-burning sheet-iron stove. The 
radiation from this stove causes the water of those boxes closest to the stove to remain 
at high temperature throughout the day and night, while those farther away are not so 
thoroughly and continually kept at as high a temperature. These feeding boxes closest 
to the stove always contain the largest terrapins in the spring, while tliose at the greatest 



THE DIAMOND-BACK TERRAPIN. 



99 



distance from the stove contain the smallest. This indicates the desirability of having 
a heating system which radiates its warmth equally and in constant and considerable 
quantity. To the commercial culturist a heating system of this kind is of prime necessity. 
The effect of winter feeding other than in its bearing on actual growth — that is, in causing 
earlier arrival at sexual maturity — will be indicated in certain of the annual brood 
studies. This is another valuable consideration for the commercial grower of terrapins. 
What gro\vth may be expected of winter-fed terrapins, compared with those that 
are allowed to hibernate, is well suggested in the records of the 1910 and 191 1 broods, 
lots of which received these treatments, respectively. The fed lots at any age are 
generally about i year's growth in advance of the hibernating lots, and in some cases 
much more. This difference in growth in 2 and 3 year old terrapins is from about 
10 to 20 mm. The difference between the average lengths of the lots diminishes as 
they pass the fourth year. From this time on the variation averages about 10 ram. 
and remains thus constant through the ninth year, if not longer (Table 3, fig. 77). 

Table 3. — Growth of Winter-fed Versus Hibernated Terrapins. 





Season of measurement 


1910 and 191 1 broods combined. 


A«c 


■RTater-ted. 


Hibernated. 


m 
years. 


Number. 


Measurement in 
millimeters. 


Ntmiber. 


Measurement in 
millimeters. 




Total. Average. 


Total. 


Average. 




fSprJne 


97 
95 
laS 
181 
j83 


3. 006 3a 9 

4. 467 47- 
7. 067 56. 5 
14. 39a 1 79. 
16. 667 1 89. 9 


98 
89 
190 
183 


" 3. 738 
3.833 
7.980 
10. 976 


27.9 
43- 

42.0 
6a3 




tFaU 




(■Sp""e 




l^uT. ...:;. :.::;;:;:::::;;;:;:;::::;::::::::■■ 




Do • 






17s 
78 
168 
167 
■ 56 
167 
89 


15.807 
8. 360 

19. 486 

20. 560 
20. 347 
33. 757 
13. 147 


90.3 
105. •» 
115. 9 
133. I 
13a 4 
136. 3 
13&.4 




\fSi7!.v.;::.:;;;:;::;;;:::::::": 


81 
309 
132 


9.315 
26, 556 
17. J77 


115. 
137. 
130. 8 




Do 




Do 




Do 


8 


Do 


30I 
136 


29.693 
17.984 


143. 7 
I4>. 7 




Do 







a Measurement of plastrons. 



MM. 
150 

140 
130 

lao 

no 

100 

90 

80 
70 
60 
50 
40 
30 
20 
10 

YfAR 





































~~~~ 









^^ 










' 


'~~ 




•*" 


—~~ 






'^~ 


^^ 


**" 


- 




















































— 


— 




— 




















- 


■- 


- 


























^ 


y 






-^ 


- 


- 


- 


- 


- 


— 


— ^ 
























- 
















^^ 


— 


,y 






■^' 














































~ 








^ 


/ 


/ 


^ 


^ 


y^ 






















































: 


^ 


^ 


- • 




/ 






























































: 








































































1 


a"^ 


3 


* 


^ 


« 


7 


8 


3 1 



IN. 
6 



FlO, 77. — Average growth ol winter-fed and Jiibeniated terrapins. Curves based on combined records ol growth of winter-fed 
and hibernated lots of the 1910 and J911 broods. , Winter-fed; hibernated. 



lOO 



BULLETIN OF THE BUREAU OF FISHERIES. 
ATTAINMENT OF SALABLE SIZE. 



The relation of age and growth to salabiHty is of importance to the prospective 
terrapin farmer, and for this purpose a table has been prepared showing the number 
and per cent of terrapins of the 1910 winter-fed and hibernating lots reaching the 5 
and 6 inch lengths at given ages (Table 4). The rate of growth of the terrapins in 
captivity is heavily retarded between the 5 and 6 inch lengths. 

Table 4. — Attainment of Marketable Size by Females op 1910 Brood. 





Six inches. 


Five inches. 


Age in years. 


Winter-led. 


Hibernated. 


Winter-fed. 


Hibernated. 




Number. 


Per cent. 


Number. 


Per cent. 


Number. 


Per cent. 


Number. 


Per cent. 






















2 in 127 
S in 133 


6.0 

a 10. 
IS- 5 
30.3 






67 in 127 52- 7 


14 in 90 
34 in 89 
45 in 78 
75 in 89 
85 in 89 


15-5 
38. a 


6 








1 in 78 

2 in 89 
4 in 89 


1. 2 

2. 3 
4.4 




1 71- 


57.6 
84. 3 
93-2 


8 


20 in 129 
25 in 129 















a Estimated. 

It will be noted that in the fifth year only 1.5 per cent of the winter-fed brood had 
reached the 6-inch length. In the sixth year 6 per cent of the brood had reached that 
length. The figures in the table appear small when a mere hundred terrapins are 
considered. To multiply them several times, however, changes them to the exact 
meaning they would have for the terrapin farmer — not merely to multiply them by 
the number of hundreds in the one brood alone, but to multiply them also by the num- 
ber of broods which contain individuals that are reaching the 6-inch mark. 

In the fifth year it appears that 52.7 per cent of the terrapins of the winter-fed 
brood has reached the 5-inch mark. Although the price paid for 5-inch terrapins in 
the market is not nearly so much as that for 6-inch, it is evident that selling when the 
5-inch mark is reached may have its value from a commercial viewpoint. It means a 
quicker turning over of the money invested and possibly a better business proposition 
when large numbers of terrapins are considered. For example, a terrapin farmer may 
rear from the eggs possibly 15,000 or more terrapins per year. Eliminate one-half (a 
much too large percentage) for death rate during the five years. Now, in the fifth 
year, 3,750 terrapins will have reached the 5-inch mark. This is approximately 300 
dozen, which, sold at $20 per dozen, bring $6,000. The market for 6-inch terrapins 
would have to be especially good to make the two or three years' extra keeping of them 
pay. However, the market for 6-inch terrapins generally pays double the amount 
paid for 5-inch terrapins, and there is the possibility that the raising of terrapins to the 
6-inch length is the more desirable business proposition, especially when it is remem- 
bered that there will be an increasing number of broods producing 6-inch terrapins 
after the enterprise has been carried for a few years, not to mention the increasing 

young production. 

CULLING. 

Each brood of newly born terrapins contains a great many which, when held in a 
warm nursery house, will not eat, or, if they do, do not make any growth. They serve 
only to bring down to a lower figure the average annual growth increment of the lot. 



THE DIAMOND-BACK TERRAPIN. 



lOI 



If, however, one selects the largest grown three-quarters of each lot, the average growth 
increment for i-year-olds is much increased. To indicate this point, a concrete example 
will best serve the purpose. There were 1,004 terrapins of the 1916 hatch placed in 
the nursery house in November, 19 16. During the following winter 500 or more of the 
same brood were allowed to hibernate, while the larger lot was fed. In May, 1917, 
the average length of the 1,004 was 39.2 mm. The best grown three-quarters, or 780 
terrapins, had an average length of 42.9 mm. The largest 200 terrapins of this lot 
averaged 54.7 mm. in length. To be compared with this lot there was still the un- 
changed fall average measurement of the hibernated terrapins, 28.1 mm. 

From this discussion it appears that it would be economical to cull the young, 
poorly grown terrapins, either to force-feed them, liberate them because of their relative 
costliness in handling, or to sell them as soon as possible after they reach the 5-inch 
length in order that all the fast-growing characteristics of the brood stock may remain 
unmixed and protected against contamination with slow-growing individuals. 

Present knowledge of the relative growths of first-year "runts" and first-year 

"selects," however, indicates that discarding or too strict culling of "runts" at the end 

of the first year is not entirely economical, since it has been learned that terrapins of 

poor first-year growth often reach in the fourth or fifth year equal length with their 

"select" brothers. It would doubtless be profitable to destroy very early any yearlings 

that show symptoms of disease unless effective remedial and prophylactic treatments 

are available. ' 

WINTER FEEDING. 

In view of the fact that in some locations favorable for terrapin culture fresh food 
may not always be available or may cost excessively, experiments have been carried 
on to learn the relative value of fresh and salt food in its assimilability and its growth- 
producing value. For this purpose one lot of newly hatched terrapins with an average 
length of 28 mm., 662 in number, was fed oysters, while another lot of the same age 
and average length, 613 in number, was fed salt fish. It appears from the following 
tabulation that the fresh-fed terrapins thrive much better than the salt fed : 







Average 


May. 1917. 


Treatment. 


Number of 
terrapins. 


length, 
Septem- 
ber. 1916. 


Average 
length. 


Maximum 
length. 


35 milli- 
meters or 
more. 


Average 
length of 
100 best. 


Salt-ted 


613 

662 


Mm. 

28.0 
28.0 


Mm. 

29-9 
33-8 


Mm. 
40.0 
Si-o 


No. 
34 
228 


Mm. 


Fresh-fed 


43.7 





The maximum length of any terrapin under our observation kept through one 
winter and until the following May in the nursery house is 81 mm." The greatest 
length of a winter-fed terrapin at approximately 2 years of age (measured in September) 
is 104 mm.," or slightly more than 4 inches. The offspring of domestic stock appear 
to do better in captivity than those of "wild" stock (fig. 78). From measurements 

> These measurements are taken on the lower shell, following the commercial method of measuring a terrapin; 8x 
inm.O= 3'.i inches: 104 mm.O 4H inches. 



I02 



BULLETIN OF THE BUREAU OF FISHERIES. 



taken in the autumns of 1919 and 1920 the following information on this point was 
brought to light : 





Numbe;;. 


Age in 

years. 


Treatment. 


October, 1919. 


Average 


Offspring o(— 


Average 
length in 
milli- 
meters. 


Maxi- 
mum 
length in 
milli- 
meters. 


length in 
milli- 
meters, 
October. 
1920. 


"Wild" stock 


95 
99 


3 
3 




65-3 

74.4 


87 
116 


66.8 




...do 


76.5 









MM. 
90 

80 

70 

60 

50 

4-0 

30 

























































y — 


— 


-- 












/-' 


^^ 






■ — 










/ 


/ 
/ 
















/ 


/ 


y 
















'' y 



































1916 



1917 



1918 



1919 



1920 



Fig. 78,— Growth of 1916 offspring of domestic and wild parentage. Each lot was fed one 
winter and selected for large size in the fall of 1917. — — — , Offspring of 1909 
domestic stock; , offspring of original Carolina wild brood stock. 

SPACE REQUIREMENT. 

The 191 7 brood had two lots of loo each chosen from it in 19 19. One of these lots, 
with average measurement of 52.5 mm., was placed in a large so-called fish pool which 
measured 38 by 24 feet. The other lot with average measurement of 60.1 mm. was 
placed in a small pen with dimensions of 29 by 12 feet. Observations on the growth of 
the two lots have been as follows : 





Square 
feet per 
terrapin. 


Number 
of terra- 
pins. 


Average length in 
millimeters. 


Increased 
length 
in milli- 
meters. 
May to 
October. 
1919. 


Average 
length 
in milli- 
meters, 
Oct. 5. 
1930. 


Increased 
length 
in milli- 
meters, 
October, 
1919, to 
October, 
- 1920. 


Treatment. 


May, 19 19. 


Oct. 23. 

1919. 




36 
9-3 


ICX3 
100 


60, I 
52- 5 


66.6 
60. 9 


6.5 
8.4 


70-3 

73.3 













THE DIAMOND-BACK TERRAPIN. 



103 



A conclusive statement of space requirement or of the value of extensive running 
ground is not warranted from this single set of observations. It is of significance, how- 
ever, that the greater growth has occurred in two successive years in the larger pool. 
This may have been due, nevertheless, as much to the fact that the terrapins were 
smaller in this pen than in the "close-confinement" pen and may have just reached or 
were in a stage of rapid growth, whereas the other group may have passed that same 
period. That plenty of space has a tendency to increase fecundity in the terrapin is 
suggested by the 1909 brood. These terrapins, held in a pen 32 by 5 feet for six years, 
have had a very large average yearly egg production per female. This pen provides 
each terrapin with approximately 26.6 square feet of ground. The exceptionally high 
laying record of these terrapins may be due, in part, to the large space and uncrowded 
condition of their pen. Their size, of course, is large, but abundant space may be a 
contributing factor in causing increased productiveness. 

1909 BROOD. 

This brood, the first terrapins hatched in captivity in the Beaufort pens considered 
in this paper, consisted of 1 2 individuals — 8 males and 4 females. Several of the males 

IN. 

G 













































l_ 


MM. 






















54 


4.2 


«U 


(8.5 


545 


/lO 


5t8 


ilJl 


32.1 


so.o 


ISO 


31.3. 


ISO 
140 












r 




^'~ 






























120 

no 








r 


1 










^ 


























109 


'^ 








so 




r 


J 


/ 






































70 
60 




I 










































SO 
40 
30 














































20 
10 



1910 1911 1912 1913 1914 1915 1916 1917 1918 1919 1920 

Fig. 79. — Growth of 1909 brood of original Carolina brood stock. Egg production and hatcfi per female 
per year expressed, respectiveli-, by figures on tlie curve. Tliis brood Itas always had but four females. 
Estimated. 

of this lot have been used in other experiments, and since 191 5 there have been only 2 
males with the 4 females under observation. They have been kept during this time in a 
small pen which, however, is large enough to support man)- more terrapins than these 6. 
This 1909 lot has hibernated each winter since its birth and shows what is probably a 
normal growth and development for terrapins held in captivity. The first eggs from the 
females of this brood were laid in 191 5 (fig. 79) when the terrapins were 6 years old. 
The egg rate per female in that season was 24. Yearly since then there has been an 
increase, until in 1919 the egg rate reached 32.2 per female. This 1919 egg production 
was accompanied by a hatch of 30 young per female and represented at that time the 
best record observed at Beaufort for average egg production and hatch. In 1920, how- 



I04 



BULLETIN OF THE BUREAU OF FISHERIES. 



ever, the brood surpassed its best record again by laying 140 eggs, of which 125 hatched 
giving an average egg record of 35 per female and an average hatch of 31.2 young per 
female. There were 16 nests found in 191 9 and 19 in 1920, indicating quite conclusively 
that all females of the 1909 brood laid at least four times and that three of them laid 
five times in 1 920. Growth after the seventh year is small, but it is attended by increasing 
fecundity. The cause of the high percentage of infertile eggs in the first year of laying 
of this brood may be due to the fact that the males of the brood were not mature. 
However, the following }ear the larger part of the eggs by far was fertile. 

1910 BROOD. 

Two lots of the 1 9 ID brood were set apart in the fall of 19 10, one fed the first winter, 
the other allowed to hibernate. A comparison of the average growth of these two lots 
indicates that the first lot, winter-fed, by average measurement, arrived at the 5-inch 

MM. 
150 
140 
130 
120 

no 
100 
90 
80 
70 
60 
50 
40 
30 
20 



1910 1911 1812 1913 1914 1915 1916 1911 1918 1919 19^0 



IN. 






















1* 


5 


IGJ 


1L8 


21.* 


laB 


2L0 


18S 


271 


23.418.617.8 


























^ 


^ 








5.7- 


4.4 


9.3- 


6.7 


2.8- 1.3 


5 

4 
3 
























/ 


13 


-yT 


5.4- 


r''- 


■;^ 


^— 










— 




















/ 


/a 


-}> 


'7^ 


■.4 


2.9 


■2.4 


5.0 


3-9 


7.]- 


5.2 


47- 


2^ 












y 


/ 


/ 


' ^ 

•* 


^ 
























- 








i 






—/■ 






























_ 


2 
1 












/ 
/ 


' 






























- 








• 


7 


































: 












































- 














































— 



Fig. 80. — Growth of 1910 brood of original Carolina brood stock. 

per year expressed, respectively, by figures on the curves. 

large size in the spring of 1914; , fed one winter; 



Hgg production and hatch per female 
, Fed two winters and selected for 



, liibernated. 



mark and to egg-laying one year before those that hibernated, and also that the egg-laying 
began at a higher rate and continued higher than that of the hibernated group (fig. 80). 
In early spring (1915) 8 males and 25 females were selected for size from the fed lot and 
kept in a separate inclosure. Their egg production in the second 3ear of their laying 
was 16.7 per female, a much greater productiveness than was made either by the ordi- 
nary lot of fed terrapins from which the selected individuals were chosen or by the lot of 
hibernating terrapins three years later in 1919. 

These facts indicate that for the commercial terrapin culturist it would pay more 
in a series of years to hold the largest and fastest growing stock as breeders rather than 
to pick here and there for his commercial sales. He could hold such brood stock over a 
long period of years and feel certain that maximum production would not come before 
at least 15 or 20 years. He would know, also, that the egg production of his breeders 
was as large as could be obtained. Thus, each year a certain number of the best grown 
females of 3 years or older could be chosen to be held as the established brood stock. 



THE DIAMOND-BACK TERRAPIN. 



105 



i'hc balance could then be used as salable stock whenever their size was great enough 
to make them marketable. This would tend, then, to the selection by the terrapin 
farmer of his best producers and fastest growers and in the course of years lead to a 
race of quick-growing, large-framed, and highly productive terrapins. 

1911 BROOD. 

The 191 1 brood has consisted of two lots of terrapins, one fed two winters and 
hibernating thereafter, the other hibernating each winter. The average growths of 
these two groups differ about 1 2 mm. at any season of any year. The tendency, however, 
as age increases, is toward a diminishing of this difference in the average growths. 
The evidence brought to light in the 1910 brood that winter feeding tends toward earlier 
productiveness is borne out in this brood also. In the fed lot the first egg laying occurred 





























1 






























.09 





.08 





5.2 


■5.0 


8.3 


-7.0 


ws, 


9.8 


8.2; 


■7.3 


















• 


• 


^ 


^ 


-^ 




.2 


0« 


2 


0« 


5.S 


2.3 

« « 






' 






r- 


.J 


/ 

/ 


/ 






















- 










f 


y 


y 


























- 






'/ 


y 


'j 






























- 








































: 



MM. 
150 

140 

130 

120 

110 

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

19U 1912 i913 1914 J915 191G 1917 1318 1919 1920 

l"lG. 81. — Growlh of 1911 brood of original Carolina brood stock. Egg production and hatch per 

female per year expressed, respectively, by figures on the curves. , Fed two winters; 

, hibernated; , estimated; * no males in this lot previous to this year; ** fertility 

modified by experimentation, 

in the fourth year, probably by only one female. Substantial output occurred in the 
sixth year with an egg rate of 5.2 per female. The first production of the hibernating 
lot occurred in the seventh year, but this was negligible — 0.2 egg per female. The second 
egg laying in the hibernating stock was likewise small, the rate per female being 2 eggs. 
This only further points out the desirability of winter feeding. It indicates, also, when 
the results are compared with the 1910 brood lot which was fed only one winter, the 
futility and extra cost of feeding terrapins more than one winter. It appears that the 
1 910 winter-fed brood has shown th^t egg production and growth from one year's winter 
feeding is much more desirable than the same from two )-ears' winter feeding when 
selection is not made of the brood stock. 

It may be added in this general connection that winter feeding does not tend 
toward the development of weaker adults nor necessarily to animals more susceptible 
to disease. It is true that young terrapins in the nursery house are subject to disease, 
and there is occasionally considerable mortality from this cause. It apparently kills 
many of those that would probably -die from inherent weakness at best. There are 



io6 



BULLETIN OI? THE BUREAU OI^ FISHERIES. 



many terrapins which suffer an attack of the disease in question and again recover 

their well-being. The subject of mortality among the young terrapins is discussed 

on page io8. 

It is of interest to note in further discussion of feeding two winters and its lack of 

advantage to the culturist the fact that, from average measurement, the hibernated 

terrapins reach the 5-inch mark approximately one year and one-half after those fed 

two winters. Referring again to the 1910 brood, the lot fed one winter reached the 

5-inch mark two years before the 1910 hibernating group. It may then, perhaps, be 

that two winters' feeding may slow down growth rather than hurry development. It 

will be noted, too, that egg production in the 1910 brood lot fed one winter is negligibly 

different as regards the year of substantial egg production from that of the 191 1 lot fed 

two winters 

1912 BROOD. 

The 1 91 2 brood was fed the first winter and allowed to hibernate each winter there- 
after. In the spring of 1914 there was made a selection of 100 each of the smallest and 

MM. 
150 

HO 

130 

120 

110 

100 

90 

80 

70 

SO 

50 

40 

30 

20 

10 

1312 1913 1914 1915 1916 1917 1918 1919 1920 

I'lG. 82.— Growth of 191 = broods of orisinal Carolina and Texas brood stocks. Eee produc- 
tion and hatch per female per year expressed, respectively, by fisrurcs on the curves. 
• , Offspring of Texas brood stock, fed one winter; , offspring of Caro- 



IN. 
6 

S 

4 
3 






























































.5 


-.0 


1.9- 


-.0 


1.7- 
4.4- 


1.0 






















y- 


^. 


, — 


-■ 


2.3 
1.6 


1.4 


2.3' 


1.9 
















y 




<f 
















- 












> 




/ 




















: 


» 2 






/ 


/ 


./ 


/ 



























1 





































Una brood stock, selected from winter-fed lot for large si/:c October i, 1913: , 

offspring of Carolina brood stock, selected from wintcr-fcd lot as runts October i. 1913. 

largest grown terrapins of the stock. These two lots were kept separately, and their 
growth and egg production to 1920 have been observed. The lot selected for large 
size after the first two years did not exhibit as unusual growth as it had in the first 
winter, while the "runts" after 1915 showed relatively much faster growth. Their 
average length in 1917 was about 10 mm. greater than the lot which had been chosen 
originally for its early rapid growth. Both lots produced eggs in the same year (1919) 
when they were 7 years old. It is of interest to note in this connection that the " runt" 
group averaged 2.3 eggs per female, while the "selects" averaged 1.6 eggs per female. 
It is suggested, then, from this brood stock that selection with a view toward 
early attainment of salable size or early and increased egg production took place at too 



THE DIAMOND-BACK TERRAPIN. 



107 



young a stage in the development of the terrapins to be of any advantage to the terrapin 
culturist. A comparison of this 191 2 study in the effect of selection with that of the 
"selects" of the 19 10 brood emphasizes this point. Selection for size occurred in the 
1 9 10 brood when the terrapins were 4 years old. The egg production from these 
"selects" was especially large. In the 1912 lot the egg production is not above normal 
for either group of terrapins fed one winter and remaining unselected. Selection as 
early as the second year is premature, since the terrapin at that age has not reached 
one-half its adult size, and there may be many influences after the second year to retard 
growth in what then appears as an exceptionally healthy and rapidly growing terrapin. 
The Texas brood of 1912, numbering 24 in 1916, 1917, and 1918, and 14 from 
1919 to 1921, has shown greater average growth and produced eggs in 1918, a year 
earlier than the Carolina terrapins of the same age. The possible earlier arrival of 
the offspring of Texas stock at sexual maturity may be hereditary in character. All 
the antecedents of this Texas stock were from the marshes of Texas, where tlie longer 
growing and laying season with the very limited hibernation period would normally 
tend toward the occurrence of an earlier maturing animal than would be found in nature 
in North Carolina. This early maturing characteristic may have become inherent in 
the Texas stock. 

1913 BROOD. 

The 19 13 brood was originally divided into two lots — one hibernated while the 
other was fed. Of the fed lot the largest 100 terrapins were selected for further 



IN. 
6 

































































- 
























., 


_ - - 


^ 


1 


.2 












r^ 


-V 


/'" 




-^ 












- 








^ 




r 
/ 



























/ 


/- 
























- 
























1 








- 



1913 1914 1915 1916 1917 1918 1919 



1920 



Mn. 

1 50 
140 
130 
120 

110 
100 
90 
80 
70 
60 
50 
40 
30 
20 
10 



I"iG. S3. — Growth of 1913 broods of original Carolina and Texas brood slocks. 
Egg production and hatch per female per year expressed, respectively, by 

figures on the curve. , Offspring of Carolina brood stock, selected 

for large size in the spring of 1914: , offspring of Texas brood stock, 

(ed one winter; , offspring of Texas brood stock, hibernated 

Study. These selected individuals at 6 years of age did not average 4K inches, 
though, of course, there were some over 5 inches in length in the lot. Neither 
had they laid any eggs. There was, however, in the seventh year a small produc- 
tion of eggs and young in this stock. Their slowTiess of growth can not be well 



io8 



BULLETIN OF THE BUREAU OF FISHERIES. 



accounted for. The severe winter of 191 7-18 may have retarded their develop- 
ment somewhat, but the retardation in the average growth curve occurs before 
that winter. It seems only further evidence that selection of the large terrapins at 
the beginning of the second year does not necessarily mean that those terrapins will 
be the largest or best producers in the fifth or sixth year; that, as has been well shown 
in the 1912 "selects" and "runts," selection of brood stock as early as the second year 
is premature. The Texas brood of 1913 does not show normal growth. Its average 
growth has, however, been better than that of the Carolina brood which received the 
same treatment. No eggs have been laid by the Texas stock. It may be that the 
retarded average growth curve of the Texas stock is due to the fact that a number of 
the larger terrapins of this lot were lost in a heavy storm in the summer of 1918. This 
would also explain the late egg laying of this group. 

1914 BROOD. 

This lot of Carolina terrapins selected in the spring of 1915 from those terrapins 
that had been fed during the previous winter has not shown more than ordinary growth 
and did not produce eggs during 1919, the fifth year of its life. In 1920, the sixth year, 























































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M M. 

130 

120 

110 

100 

90 

80 

TO 

GO 

JO 

4.0 

30 

20 

10 



1914 1915 1916 1917 1918 1919 1920 



I'JG. 84. — Growth of 1914 broods ol original Carolina and Texas brood 
stocks. Egg production and hatch per female per year expressed, 

respectively, by figures on the curve. , Offspring of Carolina 

brood stock, selected for large size in the spring of rgrs; , off- 
spring ol Texas brood stock, selected for large size in the spring of 1915. 

however, there was a small production of eggs. Early selection and the brood's later 
retardation in average growth, which has been evidenced in lots previously discussed, 
is further borne out here. The Texas brood of 19 14 has been rather insignificant, in- 
asmuch as it consisted of only five terrapins in 19 19, the others having been shipped 
to Texas. These five averaged somewhat larger than the Carolinas of the same stock, 
but had not produced eggs up to 1920. To make room for other experimental lots 
they have been shipped to Texas to be liberated. 

MORTALITY. 

As has been pointed out in the report of 19 17 mortality among adult terrapins is 
very small. It does not amount to more than one-half of i per cent. In the young 
the mortality runs higher, especially if the terrapins are winter-fed. The death rate 



THE DIAMOND-BACK TERRAPIN. IO9 

among young terrapins hibernating the first year after birth is, however, very small. 
There may be an increase during the year following, but it is negligible. The death rate 
in the nursery house, however, is a matter of importance, though in certain years it is 
small. The cause of heightened mortality in the winter-fed individuals is a disease, 
rather cancerous in nature, which attacks the head, flippers, and especially the tail of 
the terrapin. The disease rots off the tail and spreads to the body proper, probably 
affecting the spinal cord and causing paralysis and death. Often terrapins become blind 
or unable to eat because of the disease. Its cause is unknown, though it probably is 
due to a microorganism. The disease seems most virulent to those nursery boxes which 
are best heated or in the sun, while those which remain throughout the cold season in 
the shade or at a considerably lower temperature than the others do not suffer so high 
a death rate. The disease does not attack the weak and small terrapins alone, but 
often kills some of the best grown. The kind .of food used seems to have no connection 
with the prevalence or the virulence of the disease. Antiseptic washes and thorough 
cleanliness in the house and boxes apparently have some advantages, but the disease 
will prevail even when the most scrupulous care is taken. Possible value of antiseptic 
treatments seems to be borne out to some extent in the table on page 1 10. Treatments 
have been with potassium permanganate solution applied to the nursery boxes at intervals 
of a day or every few days. The solution is poured into the boxes and thrown upon the 
sides, allowed to remain some time, and then drawn off. Early in the fall before young 
terrapins are housed a thorough treatment with formalin or copper sulphate solution 
is given the boxes and walls of the house. The floor, being sand, is treated with lime. 

The first year that any antiseptic was used in the nursery house was 191 5. In 
1914 the percentage of mortality among terrapins housed for the winter was 29. In 
1915, with the disinfecting treatments being used, the mortality dropped to 5 per cent. 
However, this drop in mortality rate may have been due to causes other than the use of 
the disinfectants, for since 1915 there has been a continued high mortality rate even 
though disinfectants have been used regularly. 

Apparently the infecting organism can live in either salt, brackish, or fresh water, 
as the disease, once started, spreads when the water in the nursery boxes is changed 
from fresh to salt, or vice versa. Certain terrapins that are attacked recover after 
several weeks, but the majority die. What possibly is another symptom of the same 
disease, or perhaps another disease altogether, is the so-called "softening of the' shell" 
among the young terrapins. It is found among the terrapins that make no growth 
and is due, perhaps, to faulty absorption of the yolk sac or to possible infection of the 
body wall during this process. Such infection could be readily conveyed to the internal 
organs and destroy the health of the terrapins so affected. The "softening of the 
shell" symptom is always accompanied by loss of the power of growth and sometimes 
by the loss of pigment in the carapace or by a deadened appearance of the entire shell. 
Terrapins that develop this latter symptom rarely live. The offspring of the Texas 
stock are as susceptible to the disease as those of the Carolina. Hybrids (Carolina- 
Texas cross) are none the less susceptible to the disease. 

From a study of the winter-fed terrapins during the winter of 1919-20, it is sug- 
gested that high temperature and direct sunlight on the nursery boxes in which are held 
the several lots of yearlings are correlated closely with the prevalence of the disease. 
It appears that the greatest mortality occurred in those boxes closest to the stove and 



I lO 



BULLETIN OF THE BUREAU OF FISHERIES. 



in such locations in the nursery house that direct sunUght fell upon them. Greatest 
growth also occurs in those terrapins held closest to the heater, and therefore there 
appears to be a direct relation between rapid growth and increased prevalence of the 
disease. The mortality of winter-fed terrapins, as it has occurred during the period 
from November of one year to March of the next since 19 12, is as follows: 

Mortality of Winter-fed Terr.apins. 



1912,. 
1913. 
1914. 
191S 



Number 
fed. 



S46 

569 

I. 771 

1.493 



Mortality. 



Number. Per cent. 



41 
87 



7 

7 

.=9 

5 



1916 
1917 
1918 
1919 






Number 


Mortality. 


fed. 


Number. 


Percent, 


2. 126 
2.038 


227 
554 


10 

27 


2 937 


529 


18 



' All terrapins of the 1918 brood were liberated. 



SUMMARY. 



The egg production and the hatch of the original and second Carolina and of 
the Texas brood stocks during their captivity at Beaufort have been reviewed. It 
appears that the probable average age of individuals of the two Carolina brood stocks 
in 1 92 1 is 28+ and 18+ years, respectively. Egg production in domestic terrapins 
has occiured as early as the fourth year. In terrapins fed one or two \vinters egg pro- 
.- duction generally begins in the fifth or sixth year. In hibernating terrapins it rarely 
occurs before the seventh year. Egg production immediately after penning is small 
but increases to normal in about the third year of captivity. At least for the first six 
years of sexual maturity, probably for much longer, it is greater among the fed terra- 
pins of a certain brood than among those of the same brood allowed to hibernate. It 
is estimated that maximum egg production occurs when a terrapin is approximately 25 
years of age. 

Terrapins in captivity have been observed to lay as often as five times in a single 
season. Average annual egg productions as high as 23.6 and 24.5 per female have 
been recorded for the original Carolina stock and the Texas brood stock, respectively. 
The maximum average annual egg production of any female under observation has 
been 35 eggs; the maximum hatch per female, 31.2 young. This record was obtained 
in 1920 from the 1909 offspring of the "wild" stock. 

Rats, because of their burrowing into lately made nests and destroying large num- 
bers of eggs, are serious enemies of the terrapin. 

The proper numerical relation of males to females for maximum fertihty is not 
known exactly, and it is difficult to ascertain it accurately in view of the habit of pro- 
miscuous mating among terrapins. One mating, moreover, may give rise to fertile 
eggs for four years thereafter; that is to say, the life of the spermatozoon in the female 
after copulation may be at least four years. A 90 per cent hatch, which appears to be 
normal, can, however, be obtained among well-matured terrapins when the number of 
males is one-third the number of females. This average percentage of hatch is not 
increased bv the presence of a larger proportion of males. It appears from the study 
of certain of the domestic broods that while egg laying is small a maximum fertility may 



THE DIAMOND-BACK TERRAPIN. I 1 1 

be obtained, but not always, from broods in which there are 5 to 12 males per 100 females. 
However, when egg production is substantially increased it appears that there must be 
more males to obtain maximum fertility. Broods in which the males numbered 24 to 
32, respectively, per 100 females produced a normal fertility, even though egg production 
was large. It seems warranted, then, to conclude that from 24 to 32 males per 100 
females are necessary in order to obtain a 90 per cent fertility when the females of a 
brood average perhaps from 12 to 24 eggs per season. Males are apparently a year 
slower than the females of the same brood in coming to sexual maturity. 

The growth of terrapins from birth to their maturity is recorded. The increasing 
number and percentage of individuals of a given brood reaching the 5 and 6 inch lengths, 
the marketable size of terrapins, as age increases has been pointed out. In the sixth 
year 60 per cent of a given winter-fed lot reached the 5-uich length and 6 per cent the 
6-inch length. In the seventh year of a given hibernated lot 57 per cent of the brood 
reached the 5-inch length and i per cent the 6-inch length. 

A large number of each brood of winter-fed terrapins will have reached the 5-inch 
length by the foiu'th year. In the fifth year the average winter-fed terrapin will pass the 
5-inch mark. Winter feeding not only hastens growth but quickens development of 
the sex organs and influences toward greater fecundity at an earlier date than occurs 
among terrapins allowed to hibernate. Offspring of domestic terrapins appear to do as 
well in captivity as the offspring of "wild " stock. The maximum growth for any terra- 
pin raised in captivity under observation has been 81 mm. for. one year's and 104 mm. 
for two years' development. Small terrapins seem to make faster growth when fed 
oysters than they do when fed salt or fresh fish. Adults make good growth when fed 
fresh fish. 

Selection of brood stock should not occur before the third year, preferably later. 
Selection for this purpose should be of the largest individuals of a brood, since there is a 
positive correlation between size, age, and fecundity. Earlier selection than in the third 
year is undesirable, since rapid-growing i and 2 year old terrapins often have their 
growth retarded in the following years and at the fifth year are no larger and no more 
productive than those terrapins which were poorly grown in the first two years. 

It appears that the more space allowed terrapins in captivity the greater will be 
their growth within certain limits. Plenty of space may also have a bearing in its possi- 
ble influence on increased egg production. 

Mortahty among yearling terrapins fed in a warmed nursery house during the winter 
varied from 7 to 29 per cent from 1912 to 1919. Mortality among the adult terrapins, 
as has been pointed out in another publication, is about one-half of i per cent. There is 
no doubt that many more than one-half of the young terrapins of any brood will live 
in captivity to attain a salable size. Yearling Texas and Carolina terrapins and the 
hybrids of these stocks seem to be equally susceptible to a disease, probably bacterial, 
which has killed many young terrapins in the niu-sery house at Beaufort. Disinfecting 
treatments of the nursery house and boxes have not proved to be a consistent control 
of the disease. 



LIBRARY OF CONGRESS 



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